Investments and Marketable Securities - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Investments and marketable securities	$ 0	$ 0
Available-for-sale Securities, Gross Unrealized Gain (Loss)		0	$ 0
Proceeds from sales of investments and marketable securities	0	25,000,000	644,000,000
Available-for-sale Securities, Gross Realized Gain (Loss)	$ 0	$ 0	$ 0